gia777
Topic Author
Posts: 142
Joined: Thu Dec 03, 2015 4:12 pm

GPWS System

Thu Nov 28, 2019 2:47 am

Hi Guys I was wondering during landing approach..... how GPWS can tell the difference between landing and almost hitting a hill or ground?
Cheers,

GIA777 :coffee:
 
GalaxyFlyer
Posts: 4129
Joined: Fri Jan 01, 2016 4:44 am

Re: GPWS System

Thu Nov 28, 2019 3:29 am

Because it knows there’s a runway in front of it and using GPS knows where it is in relation to that runway. Just try landing at an airport that’s NOT in the database. It warned you unless you construct a pilot defined waypoint as the airport. Yes, I’ve had to do that.
 
Woodreau
Posts: 1825
Joined: Mon Sep 24, 2001 6:44 am

Re: GPWS System

Thu Nov 28, 2019 3:29 am

There's two basic systems - GPWS and enhanced GPWS.

the basic GPWS relies solely on the radar altimeter and guards against 7 different modes:
    Excessive descent rate ("SINK RATE" "PULL UP")
    Excessive terrain closure rate ("TERRAIN" "PULL UP")
    Altitude loss after take off or with a high power setting ("DON'T SINK")
    Unsafe terrain clearance ("TOO LOW – TERRAIN" "TOO LOW – GEAR" "TOO LOW – FLAPS")
    Excessive deviation below glideslope ("GLIDESLOPE")
    Excessively steep bank angle ("BANK ANGLE")
    Windshear protection ("WINDSHEAR")

Enhanced GPWS adds a virtual terrain database paired with aircraft position.

So when you're approaching to land, the aircraft knows you are in proximity to a landing runway and as long as you are above the terrain clearance floor, there is no terrain warning.
Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
 
GalaxyFlyer
Posts: 4129
Joined: Fri Jan 01, 2016 4:44 am

Re: GPWS System

Thu Nov 28, 2019 3:31 am

Woodreau did a much better explanation and I assumed EGPWS as conventional GPWS doesn’t care about runways.
 
RetiredWeasel
Posts: 738
Joined: Sat Jul 05, 2014 8:16 pm

Re: GPWS System

Thu Nov 28, 2019 3:55 am

There was one more with the basic GPWS which was
• aircraft not in landing configuration below 500 feet AGL

and a warning:
The GPWS is not designed to warn if either of the following occur:
• landing short i.e., the aircraft is in the landing configuration with a normal rate of
descent without an ILS glideslope
• a flight profile which approaches very steep terrain such as a cliff

Edit: On further study it looks like the "Unsafe terrain clearance ("TOO LOW – TERRAIN" "TOO LOW – GEAR" "TOO LOW – FLAPS")" that Woodeau posted is the same as the one I mentioned.
 
gia777
Topic Author
Posts: 142
Joined: Thu Dec 03, 2015 4:12 pm

Re: GPWS System

Thu Nov 28, 2019 5:18 am

GalaxyFlyer wrote:
Because it knows there’s a runway in front of it and using GPS knows where it is in relation to that runway. Just try landing at an airport that’s NOT in the database. It warned you unless you construct a pilot defined waypoint as the airport. Yes, I’ve had to do that.


So lets say there is a mountain right in front of your way.... how much time the GPWS give to the pilot to safely react? sometimes I got a feeling the gap between the warning about to hit the mountain is kind a narrow.

Last week, I was flying into an airport surrounded by hills, got me worried a bit since the weather is kinda foggy. I was wondering damn...the GPWS must sounded :)
Cheers,

GIA777 :coffee:
 
gia777
Topic Author
Posts: 142
Joined: Thu Dec 03, 2015 4:12 pm

Re: GPWS System

Thu Nov 28, 2019 5:19 am

Woodreau wrote:
There's two basic systems - GPWS and enhanced GPWS.

the basic GPWS relies solely on the radar altimeter and guards against 7 different modes:
    Excessive descent rate ("SINK RATE" "PULL UP")
    Excessive terrain closure rate ("TERRAIN" "PULL UP")
    Altitude loss after take off or with a high power setting ("DON'T SINK")
    Unsafe terrain clearance ("TOO LOW – TERRAIN" "TOO LOW – GEAR" "TOO LOW – FLAPS")
    Excessive deviation below glideslope ("GLIDESLOPE")
    Excessively steep bank angle ("BANK ANGLE")
    Windshear protection ("WINDSHEAR")

Enhanced GPWS adds a virtual terrain database paired with aircraft position.

So when you're approaching to land, the aircraft knows you are in proximity to a landing runway and as long as you are above the terrain clearance floor, there is no terrain warning.


do airlines nowadays equipped with advanced GWPS? or the old one?
Cheers,

GIA777 :coffee:
 
Airliner1973
Posts: 4
Joined: Thu Mar 14, 2019 6:48 am

Re: GPWS System

Thu Nov 28, 2019 6:17 am

I think the pilots flying for Druk Air into Paro fly with GPWS off (or so I've read somewhere) as they fly direct into the mountains to land . . . So, pilots can elect to switch it off when it becomes a nuisance . . .
 
Woodreau
Posts: 1825
Joined: Mon Sep 24, 2001 6:44 am

Re: GPWS System

Thu Nov 28, 2019 10:40 am

Going off memory, (bad idea given this crowd) because I’m about to start preflight And get a flight ready for departure.

The FAA has mandated that EGPWS be installed on airliners with more than 9 seats since mid-2000-ish so both systems are installed. But both can be MELed depending on the approved MEL.

Basic GPWS (off the radar altimeter) gave a 20ish second warning

Enhanced GPWS because it can look ahead doubles the warning and gave a 40-ish second window.

The aural warnings from both systems are identical so if you got a GPWS aural warning a pilot would not know if it comes from the GPWS or EGPWS. So training emphasizes the same GPWS escape maneuver response from either system.
Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
 
GalaxyFlyer
Posts: 4129
Joined: Fri Jan 01, 2016 4:44 am

Re: GPWS System

Thu Nov 28, 2019 2:41 pm

I don’t the times, but in the sim flying the practice escape maneuver, the windshield is filled with granite at KASE when it sounds, you fly the climb and fairly easily clear the tops. Most CFIT mountain strikes are very near the top, so there’s that. I was doing some low level photo work in a bizjet and got the uncancellable gear warning a couple of times.

Can’t say about Druk Air but a friend of mine went into Paro and didn’t turn it off. I don’t think you can turn it entirely off, just flap and GS override.
 
aeropix
Posts: 247
Joined: Mon Jun 06, 2005 2:08 pm

Re: GPWS System

Thu Nov 28, 2019 2:47 pm

Since everybody already gave complete and accurate answers, I will just make a small comment about the thread title: "GPWS" stands for "Ground Proximity Warning System" so the title of the thread translates to "Ground Proximity Warning System System".

I won't say it's right or wrong, even though I have my opinion. Just pointing it out for your own consideration. Something like,

"GPS System" that I hear often = "Global Positioning System System"
"ATM Machine" = "Automated Teller Machine Machine".

I'll leave it up to you to decide if that sounds correct, or should perhaps be just "GPWS" with no "extra" "System" or maybe use "GPW System".

Or leave it as is, your call.
 
RetiredWeasel
Posts: 738
Joined: Sat Jul 05, 2014 8:16 pm

Re: GPWS System

Thu Nov 28, 2019 4:08 pm

With the old system in 727s, (mid 90's) we would occasionally (as I recall) get a terrain warning when on final into SEL (Gimpo) for RW32L due to a hill. However on our Jep 10-7 pages for that airport it was clearly noted and I cant remember if we could silence it or just ignored it.
 
GalaxyFlyer
Posts: 4129
Joined: Fri Jan 01, 2016 4:44 am

Re: GPWS System

Thu Nov 28, 2019 4:15 pm

aeropix wrote:
Since everybody already gave complete and accurate answers, I will just make a small comment about the thread title: "GPWS" stands for "Ground Proximity Warning System" so the title of the thread translates to "Ground Proximity Warning System System".

I won't say it's right or wrong, even though I have my opinion. Just pointing it out for your own consideration. Something like,

"GPS System" that I hear often = "Global Positioning System System"
"ATM Machine" = "Automated Teller Machine Machine".

I'll leave it up to you to decide if that sounds correct, or should perhaps be just "GPWS" with no "extra" "System" or maybe use "GPW System".

Or leave it as is, your call.


I was always taught you write the acronym and add “system”, “organization” whatever following it. You don’t read out the acronym to make the word sound twice. The sentence /title sounds better that way, IMO. I’ll try find my old NYT style guide. Also, any acronym, not in common use, shall be written out entirely followed in parentheses with acronym in all caps.

GF

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